1. Field of the Invention
The present invention generally relates to an in-line resonator for an air induction system.
2. Description of Related Art
Resonators for attenuating acoustic pressure pulsations in automotive applications are well known. The air induction systems of internal combustion engines produce undesirable noise in the form of acoustic pressure pulsations. This induction noise varies based on the engine configuration and engine speed. The induction noise is caused by a pressure wave that travels from the inlet valve towards the inlet of the air induction system. Further, the induction noise may be reduced by reflecting a wave toward the inlet valve 180° out of phase with the noise wave. As such, Helmholtz type resonators have been used to attenuate the noise wave generated from the inlet valve-opening event. In addition and more recently, resonators have been developed that change the volume of the resonator to adjust for varying frequencies of the noise wave, as engine speed changes. Previous designs, however, have not provided the control of multiple frequencies at the same engine speed, which is required for some applications.
To meet order based air induction noise targets, it is generally necessary to incorporate a tuning device, such as a resonator, into the air induction system. Traditional static resonators are tuned to a fixed frequency that will not change with engine speed. These resonators provide notch-type attenuation at their designated frequency, but introduce undesirable side band resonances at higher and lower frequencies. Even after the addition of multiple static devices, it may still not be possible to match the desired order based targets due to the notch-type attenuation and side band amplification caused by such devices. Resonators have been developed that change the volume of the resonator to adjust for the varying frequencies of the noise wave as engine speed changes. However, the acoustic pressure pulsations may be composed of several frequencies of significant amplitude that occur simultaneously at any given engine speed.
In view of the above, it is apparent that there exists a need for an improved resonator having broader flexibility to attenuate the various noise frequencies of the engine.